It is well known that certain adsorbed substances may be displaced from adsorbents such as activated carbon by a still more strongly adsorbed substance; indeed, on weak adsorbents the process of adsorptive displacement is responsible for the phenomenon of solid-liquid chromatography. The criteria for displacement of one solute by another on activated carbon have recently been disclosed by Rosene and Manes (J. Phys. Chem. 80, 953 (1976)). In general, on an essentially non-polar adsorbent such as activated carbon, an adsorbate can be displaced only into a solvent in which it is soluble and usually by a displacing agent with a higher (electrical) polarizability per unit volume. For example, glucose can be displaced in water solution by p-nitrophenol. Older examples of displacement are of stearic acid by phenol in alcohol solution from activated carbon (Tiselius and Claesson, Arkiv Kemi Mineral. Geol. A16, No. 18 (1943); C. E. Dalgleish, Biochem J. 61, 334 (1955)); stearic acid is not displaced significantly in water solution because of its low solubility in water.
The removal of adsorbates from activated carbon by chemical displacement could have a number of important advantages. One is in the use of carbon in the treatment of potable waters to remove possible carcinogens and other impurities of relatively low molecular weight, such as chloroform, dichloromethane, dichloroethane, etc. Here the capacity of the carbon is relatively low and it is relatively expensive to remove the carbon for conventional thermal regeneration; an in situ process would be of considerable advantage. Another application is in the treatment of waste waters, where certain refractory adsorbates resist regeneration by thermal treatment, so that one does not recover original activity on thermal regeneration, even after allowances for furnace losses. Finally, a chemical regeneration process would be of advantage in attaining quantitative removal of expensive substances on process carbons, substances that would ordinarily be lost in thermal regeneration. The chief stumbling-block to chemical regeneration has been the problem of removing a displacing agent, since any such material would have to be more strongly adsorbed than the most strongly held adsorbate on the carbon. Finally, in the recovery of expensive substances from activated carbon, even by a process that would leave the displacing agent on the carbon, there is the problem of the potential toxicity of a displacing agent.